1. Field of the Invention
The present invention relates to a method and apparatus for cleaning a vacuum chamber used in fabricating integrated circuits, such as a chemical vapor deposition (CVD) chamber or physical vapor deposition (PVD) chamber.
2. Background of the Prior Art
In a typical CVD process adopted for manufacturing semiconductor devices, chemical reactions for depositing a desired material takes place in an enclosed processing chamber. The substrate receiving the material is typically supported on a susceptor or other substrate support member located inside the processing chamber. While the material is being deposited on the substrate, the material may also deposit as a film on the wall of the processing chamber. A residue of the material builds up corresponding to the number of substrates processed in the chamber, leading perhaps to an unstable process and typically to the generation of contaminants or particles in the chamber. Consequently, it is necessary to clean the interior of the processing chamber on a regular basis, for example by plasma discharge.
When the chamber cleaning operation is performed, the production of semiconductor devices can not continue. As a result, the effective productivity of the chamber, as measured by substrate throughput, decreases significantly. In order to increase the chamber productivity, it is necessary to quickly finish the cleaning operation and restart the production promptly after the end of the cleaning operation. Conventional plasma cleaning operations are complete, or reach an end point, when the residue is fully eliminated from the chamber as indicated by monitoring a variation in a prescribed light wavelength emitted by the plasma. However, it is difficult to correctly detect the end point of the cleaning operation using this method, because light emitted from lamps used to heat the substrate also heats, reacts with or otherwise affects the wavelength monitor.
Japanese Kokai Patent Application No. Hei 6[1994]-224163 ("the '163 patent") discloses a process that attempts to solve this problem by detecting the end point of the cleaning operation using a mass spectrometer, or by monitoring the chamber pressure using a pressure meter. According to the method disclosed, the pressure variations within the chamber during the self-cleaning operation are measured directly. For example, when a pressure meter is used, the variation in the pressure in the vacuum chamber caused by generation of the reaction product is measured using a dial gauge to detect the end point of the self-cleaning operation.
However, when a mass spectrometer is used in accordance with the '163 patent, the system for detecting the end point of the cleaning operation becomes too large for practical use in a manufacturing process. Furthermore, when the pressure measurement is performed in the vacuum chamber according to the '163 patent, only the pressure drop inside the vacuum chamber is measured. This method of detecting the end point of a cleaning reaction is impractical and can easily provide false endpoints due to normal fluctuations in the chamber pressure.
Therefore, there is a need for a device and method for practical use in semiconductor manufacturing processes that can detect the end point of a process chamber cleaning operation without the problems described above.